Foot and mouth disease - survival of the virus on fomites
- ---------------------------------
Ever since the appearance of foot and mouth disease (FMD) in the
United Kingdom, we (the Animal Biosecurity Risk Analysis section of
the Ministry of Agriculture and Forestry) have been bombarded by
phone calls, letters, faxes, and emails from members of the public
who are suddenly extremely anxious about the risk of FMD virus
arriving on these shores via fomites.
No doubt the anxiety has been fuelled by moves on the part of several
European countries to install disinfectant-impregnated mats at
airports over which passengers from UK flights have to walk, and the
banning by some countries of imports of horses because of the
purported risk of FMD virus being present in soil carried on hooves.
We considered the risk of FMD on fomites in some detail when we
carried out an import risk analysis on sheeps' wool in 1998, and it
was interesting to us how little primary research has been carried
out on this matter in the past 30 years or so.
In fact, most review papers which examine the epidemiology of FMD
appear to refer to previous reviews when considering the risk posed
by fomites, and several of these previous review papers in turn refer
to even earlier reviews. In our own risk analyses, wherever possible
we try to use primary peer-reviewed sources. We therefore found
attempting to assess the FMD-on-fomite risk to be rather frustrating.
One of the better review articles seems to be that of GE Cottral from
1969. [Cottral GE (1969). Persistence of foot-and-mouth disease virus
in animals, their products and the environment. Bulletin de L'Office
International des Epizooties, 71(3-4), 549-68.] Table XII of that
reference comprises a list of the fomites with which FMD virus has
been associated, together with the length of the risk in weeks. For
each fomite, one or more references are cited. However, a closer look
at the 15 references cited by Cottral shows the vast majority of them
are written either in German or Russian. Of the 4 that are in the
English language, one is the 1931 Fourth and Fifth Progress Reports
of the UK Foot-and Mouth Disease Research Committee, one is a chapter
in a text book on swine diseases, one is a presentation to a 1956
USDA symposium, and only one is a peer-reviewed paper.
Of those in Russian, in 1998 we did go to the trouble of getting one
paper (Gizitdinov et al, 1957) translated into English, as it looked
particularly relevant to the risk of wool that we were assessing, but
we wonder how often that happens. Rather, many review articles refer
to the Veterinary Bulletin and other abstracting sources when
referring to these papers. So my question is, where is all the
primary research to allow an objective assessment of the risk of
transmission of FMD across international borders by fomites? As far
as we can see, most such spread is by trade in live animals or animal
products, and possibly by wind under certain specific environmental
circumstances. Although there was some speculation that imported hay
or straw was a possible route of introduction of FMD into Japan in
March 2000, we are not aware of there being any objective assessment
of that pathway.
There appears little doubt that spread via contaminated fomites has
been responsible for a great deal of farm to farm spread during
epidemics (depending on the predominant production system in the
country concerned), but how are we to assess the risk posed by shoes
worn by tourists coming from infected countries, let alone the risk
posed by their tents or their socks? Perhaps experts in this area
might care to comment, and to suggest primary reference material of
relevance.
--Howard J Pharo
National Adviser, Risk Analysis
Animal Biosecurity
MAF Biosecurity Authority
Wellington
New Zealand
[Howard has presented some interesting assessments as well as
questioning the standard. If there is some accurate references, or
authorities on the issue we would appreciate knowing it. We know from
previous FMD outbreaks others would send their laundry back home in
other countries [without causing outbreaks back home]. --moderators]
-- Andre Weltman (aweltman@state.pa.us), March 26, 2001.